Composite fiber with light interference coloring function

ABSTRACT

A novel conjugate fiber with a fine and an optical interference color-generating function, suitable for application in product fields which require aesthetic qualities, the fiber being characterized by having a structure wherein an alkali-soluble polymer with a thickness of 2.0 μm or greater surrounds an alternating laminated section with a thickness of no greater than 10 μm, comprising alkali-insoluble polymer layers with different refractive indices alternately laminated parallel to the long axis direction of the flat cross-section, wherein the ratio (SP 1 /SP 2 ) between the solubility parameter value of the higher refractive index polymer (SP 1 ) and the solubility parameter value of the lower refractive index polymer (SP 2 ) is in the range of 0.8-1.1.

TECHNICAL FIELD

The present invention relates to a conjugate fiber with an opticalinterference color-generating function. More specifically, it relates toa novel conjugate fiber with an optical interference color-generatingfunction which can be used as an excellent brightening for a variety offields of use, and which can be easily obtained as a high quality finefiber having an optical interference color-generating function bytreatment with an aqueous alkali solution or the like.

BACKGROUND ART

Conjugate fibers having an optical interference color-generatingfunction, composed of mutually independent polymer layers with differentrefractive indices forming an alternating laminate, produce interferencecoloring of wavelengths in the visible light region due to thereflection and interference effects of natural light. The colordevelopment has a brightness with a metallic gloss, and produces a pureand clear color (monochromatic) with a specific wavelength, whileexhibiting an aesthetic quality entirely different from color formed bythe light absorption of a dye or pigment. A concrete example of aconjugate fiber having an optical interference color-generating functionis disclosed in International Patent Publication No. WO98/46815.

However, when it is attempted to increase the fineness of the conjugatefiber having an optical interference color-generating function asdisclosed in the aforementioned international patent publication,peeling of the alternate laminated layers may occur, or even whenpeeling does not occur the spinning condition may be impaired due todegradation of the polymer during spinning or the optical interferenceeffect may be reduced by unevenness produced during the drawing step;this has constituted an impediment against development of the fiber toproduct applications which require improved aesthetic qualities,particularly for paints which must have a fine fiber size, cut fibersfor such purposes as cosmetics and printing, and even for some filamentuses.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to solve the aforementionedproblems and provide a novel conjugate fiber which allows a fineconjugate fiber with an excellent optical interference color-generatingfunction to be obtained by post-treatment, for development in commercialfields in which aesthetic qualities are demanded.

According to research by the present inventors, it was found that evenwith a small thickness of the alternating laminated section, if thestructure includes a polymer covering the periphery then it is possibleto inhibit peeling of the alternating laminated section and improveuniformity during the drawing step, and that if the covering polymer islater removed from the conjugate fiber, it is possible to obtain astable fine conjugate fiber with an excellent optical interferencecolor-generating function.

Specifically, a conjugate fiber with an excellent optical interferencecolor-generating function according to the invention, which can achievethe object stated above, is characterized in that an alternatinglaminated section with a thickness of no greater than 10 μm, whereinalkali-insoluble polymer layers with different refractive indices arealternately laminated parallel to the long axis direction of the flatcross-section and the ratio (SP ratio) between the solubility parametervalue of the higher refractive index polymer (SP1) and the solubilityparameter value of the lower refractive index polymer (SP2) is in therange of 0.8≦SP1/SP2≦1.1, is covered with an alkali-soluble polymer witha thickness of 2.0 μm or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

Drawings (1) to (3) in FIG. 1 are schematic illustrations showing thelateral cross-sectional shape of conjugate fibers according to theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The cross-sectional structure of the conjugate fiber having an opticalinterference color-generating function according to the invention willnow be explained with reference to the accompanying drawings. Drawings(1) to (3) in FIG. 1 are schematic representations of thecross-sectional shape of different conjugate fibers of the inventionwhen cut at a right angle to the lengthwise direction, where eachalternating laminated section comprising two different alkali-insolublepolymer layers has a flat cross-sectional shape, and the two differentpolymer layers are alternately laminated with multiple layers parallelto the long axis direction of the flat cross-section (the horizontaldirection as seen in the drawing). Also, the circumference is surroundedby a covering layer composed of an alkali-soluble polymer, where (2)shows a form in which a separate alkali-insoluble protective layer isformed between them, and (3) shows a form in which the alternatinglaminated sections are simultaneously covered with an alkali-solublepolymer.

The thickness of each polymer layer in the alternating laminated sectionis preferably in the range of 0.02-0.5 μm. If the thickness is less than0.02 μm or greater than 0.5 μm, it will be difficult to achieve theexpected optical interference effect in a useful wavelength range. Thethickness is more preferably in the range of 0.05-0.15 μm. A higheroptical interference effect can be achieved if the optical distance,i.e. the product of the layer thickness and refractive index of the twodifferent components is equal. More preferably, twice the sum of the twooptical distances is equal to the length of the desired color, in orderto maximize the interference color.

The cross-sectional shape of the alternating laminate perpendicular tothe fiber axis direction of the conjugate fiber of the invention is flatas shown in FIG. 1, and it has a long axis (horizontal direction in thedrawing) and a short axis (vertical direction in the drawing). A largeflatness (long axis/short axis) of the cross-section permits a largereffective area for optical interference, and is therefore the preferredfiber cross-section form. When the flatness of the fiber cross-sectionis at least 3.5, preferably at least 4.5 and especially at least 7, itis easier to align the flat axis sides of the fibers together in theparallel direction during use, and the optical interferencecolor-generating function is improved. If the flatness is too large,however, the reeling property is notably reduced, and therefore it ispreferably no greater than 15 and especially no greater than 12. Incases where the protective layer described below composed of analkali-insoluble polymer covers the outer periphery of the flatcross-section, the protective layer section is included in calculatingthe flatness.

The number of different independent polymer layers laminated together inthe alternating laminated section, in a cross-section of the fiber ofthe invention, is preferably 10-120 layers. The optical interferenceeffect is reduced with less than 10 laminated layers. With more than 120laminated layers, however, not only can no further increase in lightreflection be expected, but the spinneret structure becomes complex andreeling is hampered, while it is not easy to satisfy the conditionsdescribed hereunder for the thickness of the alternating laminatedsection, such that the object of the invention becomes difficult toachieve.

As explained above, the cross-sectional shape of the alternatinglaminated section of the conjugate fiber of the invention is a flatshape with a plurality of polymer layers with different refractiveindices alternately laminated, and in terms of the optical interferencefunction, parallelism of the alternating laminated layers, i.e.uniformity of the optical distance of each layer in both the long axisand short axis directions of the flat cross-section, is extremelyimportant for the reflection intensity and the monochromaticity (colorgeneration clarity). In order to form a flat laminated structure with alarge interfacial area, it is important to control the laminatedlayer-forming process in the complex spinneret flow channel, the Baruseffect after discharge, interfacial tension and the like, in order torealize a uniform laminated layer thickness, and for this purpose it isessential to specify the ratio of the solubility parameter (SP value)between the layers of polymers with different refractive indices. Thatis, the ratio (SP ratio) between the solubility parameter value of thehigher refractive index polymer (SP1) and the solubility parameter valueof the lower refractive index polymer (SP2) must be in the range of0.8≦SP1/SP2≦1.1, and especially in the range of 0.85≦SP1/SP2≦1.05. Sucha polymer combination allows a uniform alternating laminated structureto be easily obtained since it reduces interfacial tension acting at theinterface when the alternating laminated layer flow of the two differentpolymers is discharged from the spinneret. On the other hand, if the SPratio is outside of the aforementioned range, the discharged polymerflow will tend to be rounded due to surface tension; moreover, shrinkageforce acts to minimize the contact area at the interface between the twopolymer laminated layers, and since the laminated structure includesmultiple layers the shrinkage force is commensurately increased,resulting in rounding as the laminated layer surfaces become curved andmaking it impossible to obtain a satisfactory flat shape. In addition,the Barus effect will become more prominent, whereby the polymer flowtends to swell after leaving the spinneret.

Examples of preferred combinations which satisfy the conditionsdescribed above include a combination of polymethyl methacrylate havingan acid value of 3 or greater with polyethylene terephthalatecopolymerized with a dibasic acid component having a metal sulfonategroup at 0.3-10 mole percent per total dibasic acid component formingthe polyester, a combination of an aliphatic polyamide with polyethylenenaphthalate copolymerized with a dibasic acid component having a metalsulfonate group at 0.3-5 mole percent per total dibasic acid componentforming the polyester, a combination of polymethyl methacrylate with anaromatic copolymer polyester copolymerized with a dibasic acid componentor glycol component having a side chain alkyl group, at 5-30 molepercent per total repeating unit, a combination of polymethylmethacrylate with polyethylene terephthalate or polyethylene naphthalatecopolymerized with 9,9-bis(parahydroxyethoxyphenyl)fluorene at 20-80mole percent per total repeating unit, a combination of an aliphaticpolyamide and polyethylene terephthalate or polyethylene naphthalatecopolymerized with 9,9-bis(parahydroxyethoxyphenyl)fluorene at 20-80mole percent per total repeating unit and a dibasic acid componenthaving a metal sulfonate group at 0.3-10 mole percent per total dibasicacid component forming the polyester, a combination of polymethylmethacrylate and a polycarbonate comprising2,2-bis(parahydroxyphenyl)propane as a dihydric phenol component, and acombination of polymethyl methacrylate and a polycarbonate comprising9,9-bis(parahydroxyethoxyphenyl)fluorene and2,2-bis(parahydroxyphenyl)propane (molar ratio: 20/80-80/20) as dihydricphenol components.

According to the invention, it is important for the thickness of thealternating laminated section to be no greater than 10 μm and preferably2-7 μm. If the thickness exceeds 10 μm, it is not possible to obtain afine conjugate fiber with an optical interference color-generatingfunction even if alkali treatment is performed, and the object of theinvention therefore cannot be achieved.

If necessary, there may also be provided on the alternating laminatedsection a protective layer composed of an alkali-insoluble polymer, witha thickness of 0.1-3 μm and preferably 0.3-1.0 μm. If this thickness issmaller than 0.1 μm the effect of the protective layer will be minimal,and if it is greater than 3 μm it will be difficult to obtain a finefiber with an optical interference color-generating function even iftreatment with an aqueous alkali solution is carried out.

There are no particular restrictions on the polymer forming theprotective layer so long as it is alkali-insoluble, but preferably ithas a solubility parameter value (SP3) at the same level as thesolubility parameter of the polymer composing both sides in the longaxis direction of the alternating laminated section (the higherrefractive index polymer or lower refractive index polymer), andspecifically 0.8≦SP1/SP3≦1.2 and/or 0.8≦SP2/SP3≦1.2 is preferred. If itis the same as the higher melting point polymer of the alternatinglaminated polymers, the protective layer section is first formed of thepolymer with the higher melting point which has the higher coolingsolidification rate during melt spinning, so that deformation of theflat cross-sectional shape due to interfacial energy and the Baruseffect can be suppressed, and the parallelism of the laminated structurecan be maintained for an improved aesthetic quality.

The conjugate fiber with an optical interference color-generatingfunction according to the invention must have the aforementioned flatlateral cross-sectional shape, and the alternating laminated sectioncomprising multiple independent polymer layers with different refractiveindices laminated alternately parallel to the long axis direction of theflat cross-section (if necessary comprising a protective layer) must becovered with an alkali-soluble polymer having a thickness of 2.0 μm orgreater, preferably 2.0-10 μm and most preferably 3.0-5.0 μm. By thusproviding a covered layer made of an alkali-soluble polymer surroundingthe alternating laminated section, it is possible to alleviate thepolymer flow distribution at the areas near the wall sides and theinterior which is received inside the final discharge opening duringmelt spinning. As a result, even with an alternating laminated sectionthickness of 10 μm or smaller, the shear stress distribution received bythe laminated section is reduced and an alternating laminate is obtainedwith a more uniform thickness of each of the layers from the outside tothe inside. Removal of the covering layer by alkali treatment of theobtained conjugate fiber can easily yield a fine conjugate fiber havingan excellent optical interference color-generating function.

If the thickness of the covering layer is too thin, i.e. less than 2.0μm, the single filament fineness of the fiber is reduced, and because ofits flat cross-section, the condition in the spinning step is lessfavorable and problems are created for handling during thepost-treatment step. When a covering layer made of an alkali-solublepolymer is provided directly surrounding the alternating laminatedsection, similar to when a protective layer made of an alkali-insolublepolymer is formed as described above, it preferably has a solubilityparameter value (SP4) at the same level as the solubility parameter ofthe polymer composing both sides in the long axis direction of thealternating laminated section (the higher refractive index polymer orlower refractive index polymer). Specifically, 0.8≦SP1/SP4≦1.2 and/or0.8≦SP2/SP4≦1.2 is preferred.

According to the invention, alkali-insoluble and -soluble polymers havea difference in alkali reduction rate of 10× or greater. Specifically,this means that the alkali-soluble polymer of the covering layerdissolves at a rate which is at least 10 times faster than that of thealkali-insoluble polymer composing the alternating laminated sectionduring the aqueous alkali solution treatment. If the dissolution ratedifference is less than 10-fold, the alternating laminated section willalso undergo corrosion during the aqueous alkali solution treatment forremoval of the covering layer, thus producing laminated layer thicknessirregularities due to randomness or swelling in the laminated section,and reducing the optical interference color-generating function.

Examples of preferred alkali-soluble polymers include polylactic acid,polyethylene terephthalate or polybutylene terephthalate copolymerizedwith polyethylene glycol, or polyethylene terephthalate comprisingpolyethylene glycol and/or an alkali metal alkylsulfonate, orpolyethylene terephthalate or polybutylene terephthalate copolymerizedwith polyethylene glycol and/or a dibasic acid component having a metalsulfonate group.

Polylactic acid is usually composed mainly of L-lactic acid, but it mayalso contain other copolymer components such as D-lactic acid in a rangethat does not exceed 40 wt %. Polyethylene terephthalate or polybutyleneterephthalate copolymerized with polyethylene glycol preferably has apolyethylene glycol copolymerization ratio of 30 wt % or greater, inorder to notably improve the alkali dissolution rate. Polyethyleneterephthalate or polybutylene terephthalate comprising an alkali metalalkylsulfonate and/or polyethylene glycol preferably comprises theformer in a range of 0.5-3.0 wt % and the latter in a range of 1.0-4.0wt %, with the average molecular weight of the latter polyethyleneglycol suitably in a range of 600-4000. Polyethylene terephthalate orpolybutylene terephthalate copolymerized with polyethylene glycol and/ora dibasic acid component having a metal sulfonate group may comprise theformer in a range of 0.5-10.0 wt % and the latter in a range of 1.5-10mole percent per total dibasic acid component forming the polyester.

The conjugate fiber having an optical interference color-generatingfunction according to the invention preferably has an elongation in therange of 10-60%, and especially in the range of 20-40%. If theelongation is too large, the tension load on the conjugate fiber maycause fiber deformation in the step of producing a textile or cutfibers, thus tending to reduce the process throughput. On the otherhand, if the elongation is too small it will be difficult for theconjugate fiber to absorb the tension load, thus tending to increasefluff and filament breakage. Even if the elongation is within thisrange, certain types of polymers exhibit increase in the birefringence(Δn) when the spun and solid-cooled conjugate fiber is drawn, and sinceit is possible to achieve an overall increase in the difference betweenrefractive indices, considering that the difference in refractiveindices of the two different polymers is the “difference in therefractive indices of the polymers plus the difference in birefringenceof the fibers”, the optical interference color-generating function isincreased.

Also, the conjugate fiber having an optical interferencecolor-generating function according to the invention preferably has aheat shrinkage of no greater than 3% at 130-150° C. If the heatshrinkage exceeds this range, fiber shrinkage and other kinds ofdeformation that lower the optical interference color-generatingfunction will tend to occur during the steps of producing variousproducts such as cloths, embroidering yarn and cut fibers for paper,paints, inks, cosmetics and the like, during use in such products, andduring maintenance of such products by ironing, etc. For example, whenthe fiber is used to produce a cloth, a shrinkage of greater than 3% at150° C. will lead to shrinkage of the fibers when ironed, tending tocause deformation of the flat cross-section and reduce the opticalinterference color-generating function. When the shrinkage isparticularly high, for example in cases where absolutely no heattreatment has been carried out for structural fixation during thereeling step, the thickness of each layer of the alternating laminatedstructure is increased and alteration tends to occur in the color phaseof the optical interference color generation itself. For use as a paint,for example, since drying and heat fixation are carried out at the sametemperature in the painting step or printing step, a similar level ofheat resistance is preferred from the standpoint of quality.

The conjugate fiber having an optical interference color-generatingfunction according to the invention as described above may be producedby the following method, for example. Specifically, following the methoddescribed in International Patent Publication 98/46815, firstalkali-insoluble polymers with different refractive indices, in acombination such that the ratio (SP ratio) between the solubilityparameter value of the higher refractive index polymer (SP1) and thesolubility parameter value of the lower refractive index polymer (SP2)is in the range of 0.8≦SP1/SP2≦1.1, are melted and discharged to form analternating laminated structure, during which time the alternatinglaminated structure is covered with an alkali-soluble polymer having ahigher alkali dissolution rate than either the higher refractive indexpolymer or the lower refractive index polymer, to obtain an undrawnfiber having a structure with the alternating laminated section coveredwith the covering layer. The single filament fineness of the undrawnfiber will differ depending on the draw ratio, and it may be as desiredso long as the fineness of the conjugate fiber with the opticalinterference color-generating function obtained after aqueous alkalisolution treatment is no greater than 4.0 dtex and preferably in therange of 0.2-3.0 dtex. The thickness of the covering layer may be asdesired so long as the thickness of the covering layer after drawing isat least 2.0 μm.

Drawing may be carried out as necessary, while the conditions thereforare not particularly restricted and may be conventionally known drawingconditions for undrawn fibers. For example, drawing may be carried outat any temperature near the glass transition temperature (Tg±15° C.) ofthe polymer with the highest glass transition temperature, which stillallows orientation of the polymer molecule chains. The temperature inthis case is the temperature of the heating medium, such as the heatingplate or heating roller. The draw ratio may be set as appropriatedepending on the degree of strength and elongation property or thermalshrinkage property to be imparted to the finally obtained drawn fiber,but in most cases drawing may be to a maximum draw ratio of 0.70-0.95.In order to improve the heat resistance, including the thermal shrinkageproperty, the drawing may be followed by heat treatment.

The conjugate fiber having an optical interference color-generatingfunction according to the invention, which has been drawn and heattreated as necessary, may be used directly as filaments, or it may becut for use as staple fibers. When staple fibers are produced they maybe cut to a length suited for the purpose, and for application in suchfields as paper, paints, inks, cosmetics and coatings, from thestandpoint of handling properties during use and the aesthetic qualityof the final product, they are preferably cut so that the fiber lengthin the fiber axis direction is longer than the short axis length of thefiber cross-section, ignoring the alkali-soluble polymer section. Theupper limit for the length will usually be about 50 mm, and particularlyfor uses involving fine dispersion such as cosmetics and paints, it ispreferably no greater than 1 mm. A shorter length is preferred so longas it is greater than the long axis length of the laminated section, andespecially a length of a few tens to a few hundred μm is preferred.

When the conjugate fiber of the invention is to be used directly asfilaments, for example, it may be employed to form a textile with adesired textile design, and then treated with an aqueous alkali solutionto remove the alkali-soluble polymer and obtain a textile materialcomposed of the fine conjugate fiber having an optical interferencefunction.

On the other hand, when it is to be used as staple fibers, for example,they may be treated with an aqueous alkali solution beforehand to removethe alkali-soluble polymer, and then utilized in various ways as fineconjugate staple fibers having an optical interference function. Also,the conjugate fiber of the invention may be treated with an aqueousalkali solution while in skein form to remove the alkali-soluble polymerat a stage prior to producing staple fibers, and then cut afterwards.

EXAMPLES

The present invention will now be explained in greater detail throughexamples. The polymer solubility parameter value (SP value) and thedimensions of the fiber cross-section mentioned throughout the exampleswere measured by the following methods.

<SP Value and SP Ratio>

The SP value is the value represented by the square root of the cohesiveenergy density (Ec). The Ec of a polymer is determined by immersing thepolymer in various solvents, and recording the Ec of the polymer as theEc in the solvent with the maximum swelling pressure. The SP values fordifferent polymers determined in this manner are listed in “PROPERTIESOF POLYMERS”3rd Edition (ELSEVIER), p. 792. For a polymer with anunknown Ec, it may be calculated from the chemical structure of thepolymer. That is, it may be determined as the sum of the Ec values foreach substituent in the polymer. The Ec values of different substituentsare listed on page 192 of the aforementioned reference. The SP ratio ofthe alternating laminated section may also be calculated by thefollowing formula.SP ratio=SP value of high refractive index polymer (SP1)/SP value of lowrefractive index polymer (SP2)<Fiber Cross-Section Measurement>

The sample fiber is affixed to a flat silicon plate and beam capsule,and embedded in an epoxy resin. Next, an ULTRACUT-S microtome is usedfor cutting in the direction perpendicular to the fiber axis to createultrathin samples with thicknesses of 50-100 nm, which are mounted on agrid. After two hours of vapor treatment with 2% osmium tetraoxide at nohigher than 60° C., an LEM-2000 transmission electron microscope is usedfor photography (20,000×) at an acceleration voltage of 100 kV. The meanthickness of each layer of the laminated structure section and thecovering layer thickness were measured from the obtained photograph.

<Optical Interference Color-Generating Wavelength and Intensity>

A sample fiber (multifilament yarn) was wound on a black board at awinding density of 40 strands/cm and a winding tension of 0.265 cN/dtex(0.3 g/de), and colorimetry was performed using a Macbeth ColorEye 3100(CE-3100) spectrophotometer, with a D65 light source. The measurementaperture was 25 mmφ for the large aperture, and the peak wavelength andreflection intensity were measured under conditions including anultraviolet light source. For the reflection intensity, the differencein reflection intensity at baseline and peak wavelength was determinedas the net reflection intensity.

Examples 1-7 and Comparative Examples 1-2

The high refractive index polymer (Polymer 1) and the low refractiveindex polymer (Polymer 2) listed in Table 1 were melt spun in such amanner as to form a structure with 21 alternating laminated sections andan alkali-soluble polymer 3 covering the periphery thereof, and thestructure was wound up at the speed shown in Table 1. The obtainedundrawn fiber was then drawn at the draw ratio listed in Table 1 toobtain a conjugate fiber having an optical interference color-generatingfunction, with the cross-sectional shape shown in FIG. 1(1). Theevaluation results are shown in Table 2. TABLE 1 High refractive Lowrefractive index polymer index polymer SP Covering layer SP SpinningProtective Polymer Polymer Ratio Polymer ratio speed Draw layer type SP1type SP2 SP1/SP2 type SP4 SPn/SP4 m/min. ratio SP3 Example 1 CopolymerPEN1 19.1 NY6 22.5 0.85 PEGPBT 20.4 0.94(1/4) 1200 2.0 — Example 2Copolymer PET2 21.06 PMMA 18.3 1.15 Polylactic acid 19.9 1.06(1/4) 2000— — Example 3 Copolymer PEN2 19.46 PMMA 18.3 1.06 Polylactic acid 19.90.98(1/4) 2000 — — Example 4 Copolymer PC 21.45 PMMA 18.3 1.17Polylactic acid 19.9 1.08(1/4) 2000 — — Example 5 Copolymer PET1 21.5NY6 22.5 0.96 Copolymer PET 20.9 1.03(1/4) 2000 1.5 — Example 6Copolymer PET3 21.06 NY6 22.5 0.94 Copolymer PET 20.9 1.01(1/4) 2000 2.0Example 7 PC 20.3 PMMA 18.3 1.11 Polylactic acid 19.9 0.92(2/4) 3000 — —Example 8 PC 20.3 PMMA 18.3 0.90 Polylactic acid 19.9 1.02(3/4) 3000 —PC(20.3) Comp. Ex. 1 PEN 18.9 PET 21.5 1.03 PEGPET 21.3 0.93(1/4) 10003.0 — Comp. Ex. 2 PS 17.4 NY6 22.2 0.77 Polylactic acid 19.9 0.87(1/4)2000 — —

The abbreviations for the polymers in Table 1 are as follows.

-   PET: Polyethylene terephthalate-   Copolymer PET1: Copolymer polyethylene terephthalate with 0.8 mole    percent 5-sodiumsulfoisophthalic acid component-   Copolymer PET2: Copolymer polyethylene terephthalate with 70 mole    percent 9,9-bis(parahydroxyethoxyphenyl)fluorene (BPEF)-   Copolymer PET3: Copolymer polyethylene terephthalate with 70 mole    percent 9,9-bis(parahydroxyethoxyphenyl)fluorene (BPEF) and 0.8 mole    percent 5-sodiumsulfoisophthalic acid component-   PEN: Polyethylene-2,6-naphthalate-   Copolymer PEN1: Copolymer polyethylene-2,6-naphthalate with 1.5 mole    percent 5-sodiumsulfoisophthalic acid component-   Copolymer PEN2: Copolymer polyethylene-2,6-naphthalate with 70 mole    percent BPEF-   PC: Polycarbonate-   Copolymer PC: Copolymer polycarbonate with 70 mole percent    9,9-bis(4-hydroxyethoxy-3-methylphenyl)fluorene (BCF)-   PMMA: Polymethyl methacrylate-   PS: Polystyrene-   NY6: Nylon-6-   PEGPBT: Copolymer polybutylene terephthalate with 50 wt % (5.2 mole    percent) polyethylene glycol of average molecular weight of 4000-   PEGPET: Copolymer polyethylene terephthalate with 10 wt %    polyethylene glycol of average molecular weight of 4000

Copolymer PET: Copolymer polyethylene terephthalate with 3 wt %polyethylene glycol of average molecular weight of 4000 and 6 molepercent 5-sodiumsulfoisophthalic acid TABLE 2 Covering Fiber propertiesafter Alternating laminated section layer Conjugate fiber alkalitreatment Polymer 2 Covering layer Total Interference Polymer 1thickness Thickness thickness Flatness thickness Laminated wavelengthColoring Flatness ratio thickness nm nm μm μm ratio μm section nmintensity % Example 1 6.8 80 85 1.7 5 4.5 11.7 no corrosion 529 16Example 2 5.3 95 110 2.3 4 4.3 10.3 no corrosion 636 18 Example 3 7.4 7073 1.5 3 5.2 7.5 no corrosion 456 20 Example 4 6.1 75 80 1.6 2 4.5 5.6no corrosion 481 19 Example 5 8.5 72 78 1.6 3 4.8 7.6 no corrosion 46610 Example 6 7.8 78 80 1.7 5 4.2 11.7 no corrosion 486 20 Example 7 6.276 80 1.4 2 4.2 5.6 no corrosion 502 17 Example 8 5.2 90 85 1.8 5 (0.7*)4.2 13.2 no corrosion 539 21 Comp. Ex. 1 8.9 70 61 1.4 3 4.8 7.4 somecorrosion 428 7 Comp. Ex. 2 1.5 120 150 2.8 5 4.8 12.8 no corrosion 4203*Protective layer thickness = 0.7 μm (Example 8)

For Example 1, polyethylene-2,6-naphthalate copolymerized with 1.5 molepercent of 5-sodiumsulfoisophthalic acid, nylon-6, and polybutyleneterephthalate copolymerized with 2.5 mole percent of polyethylene glycolof average molecular weight of 4000, were each melted at 290° C., 270°C, and 230° C., and after weighing were introduced into a spinning packand spun at 1200 m/min. The obtained undrawn filament was drawn at thedraw ratio of 2 with a preheating temperature of 60° C, and then heatset at 150° C. and wound up. The obtained conjugate fiber showed nodamage to the alternating laminated section even after alkali treatment,and the interference reflection light of the obtained conjugate fiberwas a clear green color. For Examples 2 and 3, polyethyleneterephthalate (PET) or polyethylene-2,6-naphthalate (PEN) copolymerizedwith 70 mole percent 9,9-bis(parahydroxyethoxyphenyl)fluorene (BPEF),polymethyl methacrylate (PMMA), and polylactic acid were each melted at300° C., 255° C. and 230° C., and after weighing were introduced into aspinning pack and spun at 2000 m/min. The obtained conjugate fibers allproduced fine fibers and cut fibers with excellent color-generatingperformance. For Example 4, polycarbonate copolymerized with 70 molepercent 9,9-bis(4-hydroxyethoxy-3-methylphenyl)fluorene (BCF) was usedfor spinning in the same manner as Example 2, but with a meltingtemperature of 300° C. The obtained conjugate fiber had a clear colorand strong reflection intensity. Also, the alternating laminated sectionsuffered no damage in the aqueous alkali solution treatment step. ForExample 5, PET copolymerized with 0.8 mole percent5-sodiumsulfoisophthalic acid, nylon-6, and PET copolymerized with PEGfor alkali solubility and 5-sodiumsulfoisophthalic acid, were spun atmelting temperatures of 290° C., 270° C. and 290° C., respectively, andwound up at a speed of 2000 m/min. The obtained unstretched filament waspreheated at 80° C., drawn at the draw ratio of 1.5 and heat set at 180°C. The reflection intensity was somewhat low due to a smaller refractiveindex difference compared to the other combinations, but the obtainedconjugate fiber had excellent heat resistance and strength. For Example6, PET copolymerized with 70 mole percent9,9-bis(parahydroxyethoxyphenyl)fluorene (BPEF) and 0.8 mole percent5-sodiumsulfoisophthalic acid, nylon-6, and PET copolymerized with PEGfor alkali solubility and 5-sodiumsulfoisophthalic acid, were spun atmelting temperatures of 290° C., 270° C. and 290° C., respectively, andwound up at a speed of 2000 m/min. The obtained undrawn filament waspreheated at 80° C., drawn at the draw ratio of 2.0 and heat set at 180°C. The obtained conjugate fiber had excellent reflection intensity, heatresistance and solvent resistance. For Example 7, polycarbonate (PC) andPMMA were melted at 290° C. and 255° C. while polylactic acid was meltedat 230° C., and they were weighed, introduced into a spinning pack andspun at 3000 m/min. The obtained conjugate fiber had a high degree offlatness and exhibited a strong, clear color. For Example 8, there wasformed a cross-section provided with a PC intermediate protective layerformed surrounding the PMMA/PC laminated section (FIG. 1(2)). It wasparticularly excellent from the standpoint of heat resistance. ForComparative Example 1, however, PEN and PET, which have comparable SPvalues and are expected to have excellent uniform laminate-formingability, and PET copolymerized with 10 wt % PEG, were melted at 310° C.,300° C. and 290° C., respectively, introduced into a spinning pack andspun at 1000 m/min. The spun fiber was drawn at the draw ratio of 3 withpreheating at 80° C., and heat set at 180° C. Since the dissolution rateof the covering layer in the aqueous alkali solution was at least 3times (no greater than 10 times) that of the polymers composing thealternating laminated section, alkali corrosion was observed in thealternating laminated section after treatment and the reflectionintensity was notably reduced. For Comparative Example 2, nylon-6,polystyrene and polylactic acid were melted at 270° C., 270° C. and 230°C., respectively, introduced into a spinning pack and spun at 2000m/min. Because the SP ratio for the polymers of the alternatinglaminated section was outside of the range of the invention, the layerthickness of the alternating laminated section was large, the opticalinterference color-generating function was insufficient and thereflection intensity was low, such that a clear color satisfying theobject of the invention could not be achieved.

INDUSTRIAL APPLICABILITY

The conjugate fiber with an optical interference color-generatingfunction according to the invention has satisfactory processingstability for reeling, and thus exhibits an excellent opticalinterference color-generating function even with a small alternatinglaminated structure thickness, while it is possible to easily obtain afine fiber with an optical interference function either using the fiberdirectly as filaments, or by removing the covering layer after firstcutting into staple fibers. Particularly when cut fibers of shortlengths are produced, not only is the dispersibility suitable forutilization in paints, inks, coating agents, cosmetics and the like, butthe surface smoothness of resulting products is also improved and theoptical interference color-generating function and aesthetic quality aresatisfactory.

1. A conjugate fiber with an optical interference color-generatingfunction, having an alternating laminated section with a thickness of nogreater than 10 μm, wherein alkali-insoluble polymer layers withdifferent refractive indices are alternately laminated parallel to thelong axis direction of the flat cross-section and the ratio (SP ratio)between the solubility parameter value of the higher refractive indexpolymer (SP1) and the solubility parameter value of the lower refractiveindex polymer (SP2) is in the range of 0.8≦SP1/SP2≦1.1, is covered withan alkali-soluble polymer with a thickness of 2.0 μm or greater.
 2. Aconjugate fiber with an optical interference color-generating functionaccording to claim 1, wherein the alternating laminated section iscovered with a protective layer having a thickness of 0.1-3.0 μmcomposed of an alkali-insoluble polymer.
 3. A conjugate fiber with anoptical interference color-generating function according to claim 1 ,wherein the number of layers of the alternating laminated section is 10or greater, and the flatness ratio of the flat cross-section is 3.5 orgreater.
 4. A conjugate fiber with an optical interferencecolor-generating function according to claim 1, wherein thealkali-soluble polymer is polylactic acid, polyethylene terephthalate orpolybutylene terephthalate copolymerized with polyethylene glycol, orpolyethylene terephthalate comprising polyethylene glycol and/or analkali metal alkylsulfonate, or polyethylene terephthalate orpolybutylene terephthalate copolymerized with polyethylene glycol and/ora dibasic acid component having a metal sulfonate group.
 5. A textilehaving an optical interference color-generating function, and producedby weaving a conjugate fiber having an optical interferencecolor-generating function according to claim 1, and then treating itwith an aqueous alkali solution.
 6. Cut fibers having an opticalinterference color-generating function, and produced by cutting aconjugate fiber having an optical interference color-generating functionaccording to claim 1, in such a manner that the fiber length in thefiber axis direction is longer than the short axis direction of thefiber cross-section, ignoring the alkali-soluble polymer section.
 7. Cutfibers having an optical interference color-generating function, andproduced by treating cut fibers according to claim 6 with an aqueousalkali solution.
 8. Cut fibers having an optical interferencecolor-generating function, and produced by treating a conjugate fiberhaving an optical interference color-generating function according toclaim 1 with an aqueous alkali solution to remove the alkali-solublepolymer, and then cutting it in such a manner that the fiber length inthe fiber axis direction is longer than the short axis direction of thefiber cross-section.
 9. A conjugate fiber with an optical interferencecolor-generating function according to claim 2, wherein the number oflayers of the alternating laminated section is 10 or greater, and theflatness ratio of the flat cross-section is 3.5 or greater.
 10. Aconjugate fiber with an optical interference color-generating functionaccording to claim 2, wherein the alkali-soluble polymer is polylacticacid, polyethylene terephthalate or polybutylene terephthalatecopolymerized with polyethylene glycol, or polyethylene terephthalatecomprising polyethylene glycol and/or an alkali metal alkylsulfonate, orpolyethylene terephthalate or polybutylene terephthalate copolymerizedwith polyethylene glycol and/or a dibasic acid component having a metalsulfonate group.
 11. A conjugate fiber with an optical interferencecolor-generating function according to claim 3, wherein thealkali-soluble polymer is polylactic acid, polyethylene terephthalate orpolybutylene terephthalate copolymerized with polyethylene glycol, orpolyethylene terephthalate comprising polyethylene glycol and/or analkali metal alkylsulfonate, or polyethylene terephthalate orpolybutylene terephthalate copolymerized with polyethylene glycol and/ora dibasic acid component having a metal sulfonate group.
 12. A textilehaving an optical interference color-generating function, and producedby weaving a conjugate fiber having an optical interferencecolor-generating function according to claim 2, and then treating itwith an aqueous alkali solution.
 13. A textile having an opticalinterference color-generating function, and produced by weaving aconjugate fiber having an optical interference color-generating functionaccording to claim 3, and then treating it with an aqueous alkalisolution.
 14. A textile having an optical interference color-generatingfunction, and produced by weaving a conjugate fiber having an opticalinterference color-generating function according to claim 4, and thentreating it with an aqueous alkali solution.
 15. Cut fibers having anoptical interference color-generating function, and produced by cuttinga conjugate fiber having an optical interference color-generatingfunction according to claim 2, in such a manner that the fiber length inthe fiber axis direction is longer than the short axis direction of thefiber cross-section, ignoring the alkali-soluble polymer section. 16.Cut fibers having an optical interference color-generating function, andproduced by cutting a conjugate fiber having an optical interferencecolor-generating function according to claim 3, in such a manner thatthe fiber length in the fiber axis direction is longer than the shortaxis direction of the fiber cross-section, ignoring the alkali-solublepolymer section.
 17. Cut fibers having an optical interferencecolor-generating function, and produced by cutting a conjugate fiberhaving an optical interference color-generating function according toclaim 4, in such a manner that the fiber length in the fiber axisdirection is longer than the short axis direction of the fibercross-section, ignoring the alkali-soluble polymer section.
 18. Cutfibers having an optical interference color-generating function, andproduced by treating a conjugate fiber having an optical interferencecolor-generating function according to claim 2 with an aqueous alkalisolution to remove the alkali-soluble polymer, and then cutting it insuch a manner that the fiber length in the fiber axis direction islonger than the short axis direction of the fiber cross-section.
 19. Cutfibers having an optical interference color-generating function, andproduced by treating a conjugate fiber having an optical interferencecolor-generating function according to claim 3 with an aqueous alkalisolution to remove the alkali-soluble polymer, and then cutting it insuch a manner that the fiber length in the fiber axis direction islonger than the short axis direction of the fiber cross-section.
 20. Cutfibers having an optical interference color-generating function, andproduced by treating a conjugate fiber having an optical interferencecolor-generating function according to claim 4 with an aqueous alkalisolution to remove the alkali-soluble polymer, and then cutting it insuch a manner that the fiber length in the fiber axis direction islonger than the short axis direction of the fiber cross-section.